The present invention relates to the protection of electrical circuits and, more particularly, to the detection of arcing faults in an arcing fault protection assembly for mounting in an electrical outlet, as well as in additional electrical devices connected in parallel downstream from the electrical outlet which mounts the arcing fault detection assembly.
The electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The power is then routed through protection devices to designated branch circuits supplying one or more loads. These protection devices are typically circuit interrupters, such as circuit breakers and fuses, which are designed to interrupt the electrical current if the limits of the conductors supplying the loads are surpassed.
Although circuit breakers are a preferred type of circuit interrupter because they protect a number of outlets simultaneously, ground fault detectors in electrical receptacles or outlets have become increasingly popular in areas where a short circuit caused by contact with water is a possibility, e.g., in bathrooms and kitchens.
Typically, ground fault detectors interrupt an electric circuit due to a disconnect or trip condition such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the breaker for a time interval determined by the trip current. A ground fault trip condition is created by an imbalance of currents flowing between a line conductor and a neutral conductor which could be caused by a leakage current or an arcing fault to ground.
Arcing faults are commonly defined as current through ionized gas between two ends of a broken conductor or at a faulty contact or connector, between two conductors supplying a load, or between a conductor and ground. Arcing faults, however, may not cause a conventional circuit breaker to trip. Arcing fault current levels may be reduced by branch or load impedance to a level below the trip curve settings of the circuit breaker. In addition, an arcing fault which does not contact a grounded conductor, object or person will not trip a ground fault protector.
There are many conditions that may cause an arcing fault, for example, corroded, worn or aged wiring, connectors, contacts or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. These faults may damage the conductor insulation and cause the conductor to reach an unacceptable temperature.
It is an object of the present invention to provide an arc fault detection system and method which reliably detects arc fault conditions which may be ignored by conventional circuit interrupters.
Another object of the invention is to provide an arc fault detection system which utilizes highly reliable electronic signal processing components, so as to be relatively simple and yet highly reliable in operation.
Other and further objects and advantages of the invention will be apparent to those skilled in the art from the present specification taken with the accompanying drawings and appended claims.
In accordance with one aspect of the invention, there is provided an arcing fault protection assembly comprising a sensor, a broadband noise circuit, a controller and an electrical device. The sensor detects a current and develops a corresponding sensor signal. The broadband noise circuit determines the presence of broadband noise in the sensor signal and produces a corresponding output signal. The controller processes the sensor signal and the output signal in a predetermined fashion to determine whether an arcing fault is present. The sensor, the broadband noise circuit and the controller are mounted to the outlet receptacle or to an outlet box which houses the receptacle. The electrical device is connected in parallel to the first electrical outlet on the load side of the sensor.
In accordance with another aspect of the invention, there is provided a method of determining, at an electrical device, whether arcing is present. The method comprises the steps of sensing a current at an outlet connected in parallel to the electrical device and developing a corresponding sensor signal, determining the presence of broadband noise in the sensor signal and producing a corresponding output signal, and processing the sensor signal and the output signal in a predetermined fashion to determine whether an arcing fault is present.
The above summary of the present invention is not intended to represent each embodiment, or every aspect of the present invention. This is the purpose of the figures and detailed description which follow.